1. Field of Invention
The present invention is directed to the conversion of remote natural gases into saleable transportation fuels and petroleum products. More specifically, this invention is directed to upgrading by, for example, hydrotreating, hydrocracking and hydrodewaxing Fischer-Tropsch and/or petroleum-derived naphthas and distillates for use in saleable transportation fuels and petroleum products.
2. Description of Related Art
The Fischer-Tropsch reaction is a well known reaction, and catalysts and conditions for performing Fischer-Tropsch reactions are well known to those of skill in the art, and are described, for example, in EP 0 921 184A1, the contents of which are hereby incorporated by reference in their entirety. The Fischer-Tropsch process converts synthesis gas into linear hydrocarbons(n-paraffins, linear olefins and minor amounts of fatty acids). Due to the linear nature of such products, once they have been subjected to removal of heteroatoms and isomerization, they are well-suited for use in various transportation fuels and other saleable petroleum products including, but not limited to, jet fuels, diesel fuels and petrochemical feedstocks including, but not limited to, benzene, toluene and xylene.
However, lighter naphtha fractions are generally poorly suited for use in conventional gasolines because their linear nature causes them to exhibit a very low octane rating. Further, although naphtha can be used as a petrochemical feedstock for ethylene production, naphtha has not been found to be suitable for transportation fuels. In addition, even though naphtha may be suitable as a fuel for fuel cell vehicles, because fuel cell vehicles have not yet become widely used, a need still exists for a process to convert naphtha so that it can be used in conventional transportation fuels.
In addition to the need to convert the naphtha fraction of a Fischer-Tropsch process, there is also a need to upgrade (e.g., hydrotreat, hydrocrack or hydrodewax) heavier boiling distillates from the Fischer-Tropsch process so that they are acceptable for use in transportation fuels and other saleable petroleum products.
More specifically, products of the Fischer-Tropsch process, in finished products, exhibit boiling ranges having unacceptable levels of oxygenates and olefins (alcohols and traces of acids). Also, the content of linear hydrocarbons in such products is so high that the resulting products exhibit unacceptable cold climate properties including, but not limited to, jet freeze point, diesel cloud point, and lube base stock pour point. Traditionally, these products can be upgraded to obtain saleable transportation fuels and lube base stocks by employing various processes including, but not limited to, hydrotreating, hydrocracking, hydrodewaxing, combinations thereof and the like.
Although such processes can upgrade Fischer-Tropsch products suffering from the above-mentioned problems to obtain saleable transportation fuels and other petroleum products, the disadvantage of these processes is that they require hydrogen. That is, in order to perform the above processes, hydrogen must be separately supplied during the application of these processes to successfully upgrade Fischer-Tropsch products. Although hydrogen can be obtained from synthesis gases, hydrogen can only be obtained from synthesis gases by employing expensive separation processes. Expensive separation processes are necessary to ensure that the hydrogen remains separate from carbon oxides that can otherwise poison catalysts used in hydrotreating, hydrocracking and hydrodewaxing processes. In addition, hydrogen can be supplied from a separate facility that reforms natural gas into hydrogen using stream reforming processes. Unfortunately, the construction and operation of a separate hydrogen production facility is extremely costly. As a result, there is an urgent need for a relatively low-cost source of hydrogen to be used in upgrading processes including, but not limited to, hydrotreating, hydrocracking and hydrodewaxing operations, so that Fischer-Tropsch products can be more inexpensively upgraded to obtain saleable products.
Another problem encountered during upgrading of Fischer-Tropsch distillates is that the stocks created do not contain sulfur but do contain oxygenates. The least expensive catalysts for hydrotreating, hydrocracking and hydrodewaxing use sulfided Group VI and VIII metals including, but not limited to, nickel, cobalt, molybdenum, tungsten, combinations thereof and the like. Non-sulfided catalysts for hydrotreating, hydrocracking and hydrodewaxing are available but are based on expensive noble metals including, but not limited to, platinum, palladium, combinations thereof and the like. Unfortunately, when sulfided catalysts are in the presence of oxygenates and in the absence of sulfur, the oxygen in the feedstock replaces sulfur on the catalyst, leading to a decline in the catalyst's performance. Decreases in catalytic performance can appear in various forms including, but not limited to, decreased activity, selectivity and/or stability. To prevent such a decline in performance, manufacturers typically add a sulfur compound to ensure that the catalyst remains adequately sulfided. Usually, the sulfur compound that is added is a pure chemical such as, for example, a dimethyldisulfide. Unfortunately, pure chemicals are expensive to purchase and require special handling that can create safety concerns and can generate additional costs. As a result, there is an need for a process that maintains sulfided catalysts in their active sulfided state without having to use chemicals.
Finally, there is also a desire for a process for upgrading (e.g., hydrotreating, hydrocracking or hydrodewaxing) petroleum-derived hydrocarbon products that are produced along with natural gases. Petroleum-derived hydrocarbon products produced along with a natural gas can include condensates, naphthas and distillates. These products have chemical compositions that are analogous to compositions of conventional petroleum products, and include a mixture of a variety of hydrocarbons including, but not limited to, linear paraffins, iso-paraffins, cyclo-paraffins, aromatics, mixtures thereof and the like. They also contain sulfur and nitrogen impurities that must be removed to obtain saleable products.